Methods
Pregnant women with HELLP syndrome with or without preeclampsia as well as features of AFLP at our referral institution between 2011 and 2018 were prospectively enrolled. At admission serum levels of sFlt-1 and PLGF were measured using electro-chemiluminescence immunoassays (ELECSYS; Roche Diagnostics GmbH, Mannheim, Germany) on Cobas e 601 analyzer (Hitachi High Technology Co, Tokyo, Japan). Dilutional series were performed using human serum in a ratio of 1:10 in patients with sFlt-1 values beyond the detection limit of 85.0 ng/ml. Clinical and obstetrical data were retrieved from patient charts.
HELLP syndrome was defined according to Tennessee and Mississippi classification as lactate dehydrogenase (LDH) ≥600U/l as a surrogate marker of haemolysis, alanine and aspartate transaminase (ALT/AST) ≥70U/l for elevated liver enzymes. We included only patients having platelets count of less than 100G/l according to the statment of ISSHP and the guideline of the German Society of Gynecology and Obstetrics18, 19. Hence, class 3 of the Mississippi classification (platelet 100 to 150 G/L) was not taken into account, as it is considered more as a transient form of HELLP syndrome.18
Preeclampsia was defined, according to the revised statement of the international society for the study of hypertension in pregnancy (ISSHP) 2014, as chronic or gestational hypertension (blood pressure ≥140/90mmHg in at least two measurements) accompanied by significant proteinuria (≥300mg/24h) or signs of utero-placental dysfunction with fetal growth restriction (FGR) or maternal endothelial dysfunction.3 According to this ISSHP statement, patients were considered suffering from a severe preeclampsia when showing severe hypertension (≥160/110mmHg), signs of impending eclampsia (headache, visual disturbances) or when diagnosed with HELLP syndrome.
Fetal growth restriction (FGR) was defined as fetal abdominal circumference <5th percentile or estimated fetal weight <10th percentile for gestational age with altered fetal and/or maternal hemodynamic or an abnormal growth trajectory over time.20, 21
We used the Swansea criteria as a diagnostic tool for AFLP. Patients were considered being positive if at least 6 criteria were present.5 To correct for gestational age-dependent angiogenic profile pattern, the time points of blood draw were matched (± 1 week) and each AFLP case was matched with two patients with HELLP syndrome with and without preeclampsia.
Statistical analysis was performed with GraphPad Prism version 8.0 for Windows (GraphPad Software, San Diego, CA, USA). Continuous variables were analysed using parametric and nonparametric tests. Proportions were analysed using Chi2-test or Fischer’s exact test where appropriate. Correlations between numerical parameters were analysed using the Spearman’s rho bivariate correlation test. A receiver operating characteristic (ROC) curve analysis was used to describe the relationship between sensitivity and false-positive rate for different angiogenic values to predict AFLP. A p-value of <0.05 was considered for significancy. The study was approved by the institutional ethics committee of the canton of Bern (Kantonale Ethikkommission Bern, Ref.-Nr.: 365/15).